With two deployments in Iraq and Afghanistan under his belt, the 25-year-old Harris was "an exceptional leader," Dennis tells NPR's Renee Montagne — the Marine chosen to be first off the chopper in an assault on a Taliban stronghold that would become a brutal firefight. "'He was this courageous platoon leader who was at the tip of the spear of this entire battle."

Six months later, watching a contingent of returning Marines step off the buses in North Carolina for a reunion with their families, Dennis realized that Nathan Harris wasn't among them. He'd been hit two weeks before — shot in the hip by a Taliban machine-gun round. He'd nearly bled to death.

"He was in extreme pain and distress," Dennis recalls. "And feeling very guilty for having left his men behind."

Harris' agonized struggle to transition back into a society that didn't much understand what he'd been through became the focus of Dennis' documentary Hell and Back Again, which won a World Cinema Grand Jury Prize at this year's Sundance Film Festival.

"It makes me want to lose my frickin' mind," Harris says in the film. "It's just like, 'My God, I would rather be in Afghanistan, where it's simple.' When you come home, it's almost more difficult than doing that stuff."

Simple? In a sense.

"Back in Afghanistan, it's simply walking, fighting and do it again the next day," Dennis explains.

But not uncomplicated. Embedded with Harris's unit, Dennis went through multiple combat engagements with the Marines. His camera captures the chaos of battle up close — dirt sprays the lens when a rocket-propelled grenade detonates nearby, and the day darkens when an IED explodes, enveloping the unit in dust and uncertainty.

"When you're exposed to that much violence and that much trauma, it's a very natural response for your body to go into this emotionally numb state," Dennis says. "You have to. When you get home, that's when it comes back — and so I'm trying to blend these two worlds, Afghanistan and North Carolina, and seamlessly create one experience to show that the fighting doesn't stop when you get back."

To create that "one experience," Dennis overlays footage from Harris' daily life in North Carolina with audio from battles the two went through in Southern Afghanistan. In one scene, Harris' wife orders corn dogs and fries from a fast-food drive-thru, as the roar of jet engines, the beat of helicopter blades and the chap-chap-chap of machine-gun fire slowly drowns her out.

Those scenes aren't literal depictions of what was going through Harris' mind in those moments. They're more impressionistic.

"Sgt. Harris and I never sat down and looked at the footage I was shooting," Dennis says. "He just had to trust me to tell his story. And so I think I brought in a lot of my own personal experiences of what it was like to come home from war — of how that way stays with you, the things that you've seen stay with you. And they change you."

Much of the film is literal, though, a chronicle of how the war changed Harris. In a pharmacy, picking up her husband's powerful medications, Ashley Harris speaks of the stranger she sometimes sees behind Nathan's eyes.

"He gets so mad, he turns into a different person almost. ... It's like I don't even see my husband; it was almost like someone had taken over him."

Wounded though he may be, Nathan Harris is still an active-duty Marine, part of the Wounded Warriors Regiment at Camp Lejeune. Dennis says he wants to go back to the battle — "he wants to be a leader of men."

It's unlikely to happen, and Harris eventually realizes that. "And so Ashley, in one way, is relieved," Dennis says. "But at the same time, I think they both wonder, 'What is he gonna do?' Nothing really seems to have the same sort of purpose or meaning once you've been over there. And so he's sort of in this transition still, two years later, [discovering] what it means to come home from war where there isn't a clear spot for you to land."

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